tanα=3,则sin2α-cos2α的值是?

tanα=3,则sin2α-cos2α的值是?
tanα=3,则sin2α-cos2α的值是?

tanα=3,则sin2α-cos2α的值是?
sinα/cosα=tanα=3
sinα=3cosα
代入sin²α+cos²α=1
所以cos²α=1/10
sinαcosα=3cosαcosα=3cos²α=3/10
则原式=2sinαcosα-(2cos²α-1)
=3/5--(-4/5)
=7/5